There has been a rapid increased demand for refrigeration systems that can attain a very low temperature range. One type of system that CaO reach such temperatures is called an ultra low refrigeration system or called an ultra low freezer, which can maintain a very low range of temperatures. The ultra low temperature refrigeration systems can be used to store and protect a variety of objects including critical biological samples so that they are safely and securely stored for extended periods of time. However, with the low storage temperatures involved and the need to periodically insert and remove particular samples from the freezer compartment, various problems may arise.
Generally, in refrigeration systems, a refrigerant gas is compressed in a compressor unit. Heat generated by the compression is then removed generally by passing the compressed gas through a water or air cooled condenser coil. The cooled, condensed gas is then allowed to rapidly expand into an evaporating coil surrounding a refrigerator or freezer compartment where the gas becomes much colder, thus cooling the coil and the compartment of the refrigeration system or freezer around which the coil is placed.
Ultra-low and cryogenic temperatures ranging from approximately −95 degrees Celsius to −150 degrees Celsius have been achieved and even as low as −160 degrees Celsius. Examples of Ultra low temperature refrigeration systems are shown, for example, in U.S. Pat. No. 6,631,625 for Non-HCFC Refrigerant Mixture For An Ultra-Low Temperature Refrigeration System and U.S. Pat. No. 6,990,819 for Dryer System For The Prevention Of Frost in An Ultra Low Temperature Freezer. U.S. Pat. Nos. 6,631,625 and 6,990,819 are now hereby incorporated by reference.
During normal operation, freezers accumulate frost as a result of humid air entering the freezer. This problem is especially critical in ultra-low temperature freezer as the samples stored in such freezers can be particularly sensitive to changes in the environment within the freezer. This is even more a problem when there is a large temperature variation. The frost that is developed, even in the smallest amounts, can affect the environment of some or all of the individual samples within the freezer compartment and, therefore, contribute to serious problems. There is a need for having greater control of the environment within such a freezer, especially a control of the frost conditions that can develop with everyday use of such a freezer.